1. Field of the Invention
The present invention concerns specific new compounds, cathode material comprising the new compounds, batteries and lithium-cells comprising said new compound or cathode material, a process for the production of the new compound and their use.
2. Discussion of Background Information
Rechargeable lithium ion batteries will play an essential role for future sustainable electrochemical energy storage strategy. The key challenges for future high-energy and/or high-power automotive applications as well as for large-scale stationary energy storage systems are high performance electrode materials.
State-of-the-art commercial cathode materials such as LiCoO2, LiFePO4, LiMn2O4 and LiMn1.5Ni0.5O4 have low capacity of lower than 170 mAh/g and low energy density of lower than 500 Wh/kg (Melot et al, Acc. Chem. Res. 2013, 46, 1226; Goodenough et al., J. Am. Chem. Soc. 2013, 135, 1167; Zhong et al., J. Electrochem. Soc. 1997, 144, 205.)
Layered cathode materials LiCo1/3MN1/3O2 (referred to as NMC) with higher capacity of 190 mAh/g have been developed. (T. Ohzuku et al., Chem. Lett. 2001, 30, 642.) A further optimization performed at the Argonne National Laboratory leads to high capacity (250 mAh/g) lithium-manganese-rich NMC composite cathodes. (U.S. 66/677,082 and U.S. Pat. No. 6,680,143; Thackeray et al, J. Mater. Chem. 2005, 15, 2257).
This high-capacity cathode material suffers from voltage fading at higher current rates and capacity fading upon high voltage (up to 4.9 V) cycling. Higher capacity cathode materials are desirable for many commercial applications. Vanadium-based materials have received considerable attention for lithium (ion) batteries due to the facts that (i) vanadium is cheap and abundant, (ii) vanadium has relatively low atomic mass, (iii) vanadium has multiple oxidation states and the redox operating voltage (typically <4.5 V) of vanadium-based materials is typically within the stability limit of conventional electrolyte, and (iv) vanadium oxides have rich crystal structures (Chernova et al., J. Mater. Chem. 2009, 19, 2526).
The ability of layered V2O5 for Li+ insertion has been well characterized. Intercalation of one Li+ per formula unit corresponds to a specific capacity of 147 mAh/g.
Further Li+ ions (X>1 in LixV2O5) insertion causes irreversible structural transformations (Delmas et al., Solid State Ion. 1994, 69, 257).
In addition, the voltage plateaus for the V5+/V4+ and V4+/V3+ redox reactions occur successively during Li+ intercalation-extraction processes (Hu et al., Angew. Chem. Int. Ed. 2009, 48, 210). This successive redox couples cause complications in designing battery systems.
Layered LiV3O8 is capable of storing reversibly two additional Li+ per formula unit, involving only V5+/V4+ redox couple (Pistoia et al, J. Electrochem. Soc. 1985, 132, 281). Rock-salt structure Li4V3O8 appears when further lithiation proceeds, which causes deterioration in the rechargeability (Picciotto et al., Solid State Ion. 1993, 62, 297).
Recently, a lithium-rich Li2VO3 vanadate with rock-salt structure has been reported with excellent cyclability and a specific capacity of 253 mAh/g by utilizing V5+/V4+ redox couple reactions (Pralong et al, Chem. Mater. 2012, 24, 12). This material was obtained by electrochemical lithiation of a monoclinic LiVO3.
One disadvantage of the above mentioned vanadium-based materials (vanadium oxides, lithium vanadates) is that they are restricted for a one-electron reaction per transition metal. Another disadvantage is that most of the materials require lithium source from anode side and thus make industrial use difficult.
Fluorine-doped materials have been applied in energy storage in order to improve the material performance and stability through surface fluorination and bulk doping (by substitution fluorine for oxygen in oxide-based materials). Fluorine-doped materials exhibit intrinsic stability in electrochemical system, such as the practical use of fluorine-based electrolytes and binders. Owing to the extraordinary electronegativity of fluorine, the M (metal)-F bonds have higher ionicity than the M-O bonds. Fluorinated LiMO2, NMC, phosphates and spinel LiMn2O4 have thus been developed and shown enhanced electrochemical performances. (Amatucci et al., J. Fluorine Chem. 2007, 128, 243.)
The structural and magnetic properties of F-doped LiVO2 (LiVO2−xFx with x=0; 0,1; 0,2 and 0,3)) have been characterized by Li et al. (Mater. Res. Soc. Symp. Proc. Vol. 1344, 2011). The use of lithium containing metal-halogen oxide as active material of a positive electrode was disclosed in JP H07 343 A.
Intercalation cathode materials enabling beyond one Li+ storage per transition metal are attractive and competitive for Li-ion batteries in comparison with conversion cathodes (high capacity, but low work voltage and relatively poor cyclability) (Poizot et al, Nature 2000, 407, 496). To date, polyanion-type intercalation cathodes Li2MSiO4 silicates (Islam et al, J. Mater. Chem. 2011, 21, 9811) and Li2MP2O7 pyrophosphates (Nishimura et al., J. Am. Chem. Soc. 2010, 132, 13596) have attracted tremendous attention in view of two-electron reaction and higher lithiation voltage. However, practical electrochemical performance of these materials shows that only one Li+ capacity can be obtained for Fe-based compounds and Mn-based materials suffer from server Jahn-Teller distortion.
In conclusion the prior art electrode materials exhibit various drawbacks and disadvantages.
Therefore, it has been the object of the present invention to provide new compounds for electrode materials, new cathodic materials, new batteries and/or lithium cells and new methods for manufacturing these subjects matter which no longer exhibit the drawbacks and disadvantages of the prior art set out about above.
In particular, the new compounds should be suitable as high performance electrode materials.
A further object of the invention was to provide batteries and/or lithium cells which allows the use of a broad range of anode materials, in order to adapt the anode material to the needed requirements. The new cathode material has to be compatible with the other materials of the cells or batteries.
A further object was to provide a method for the production of such an electrode material. The method should be easily accessible and allow the production of electrodes in high quantities and for industry scale applications.
Additionally, the battery materials should exhibits commonly improved Li storage performance as compared to the state-of-the-art.
High performance electrode materials are defined according to the invention as materials being suitable as electrode materials with high-capacity (>150 mAh/g), high current rate (>5.0 mA/g), high energy density (>500 Wh/kg) and/or current rate of at least 5 mA/g. In case of rechargeable devices a high cycling stability (at least 10 galvanostatical charge/discharge cycles). These features should be present at standard room temperature (25° C.) as well as at lower or higher temperatures (+40° C.).